1. phrasal verb
To rein in something means to control it.
[V P n] ⇒ His administration's economic policy would focus on reining in inflation.
[V n P] ⇒ Mary spoiled both her children, then tried too late to rein them in.
2. phrasal verb → rein If you rein in a horse, you stop it or cause it to go more slowly by pulling its reins.
[V P] ⇒ The horsemen reined in and shouted at the men behind to turn back.
[V P n (not pron)] ⇒ Mrs Glick reined in the horse and stopped at the crossroads. [Also V n P]
COBUILD Advanced English Dictionary. Copyright © HarperCollins Publishers